In the parable of The Sower, our Lord speaks of four different "kinds" of people who hear.
First, are those people who hear the gospel and do not believe at all (the path).
Second, are those people who hear the gospel and believe, but only until persecution comes and they fall away from Christ entirely (the rocky ground).
Third, are those people who hear the gospel and believe, but only until the cares, riches, and pleasures of this world finally smother their faith and they fall away from Christ entirely (the thorny ground).
Fourth, are those who hear the gospel and believe, holding it firm, and with great patience bear fruit (the good soil).
The one who is "good soil" is the one who hears the gospel of Christ crucified for sinners, believes he has that forgiveness, and holds this word of Christ firm (no matter what persecution or prosperity may come). In so doing, he bears much fruit.
The purpose of Christ's teaching in this section of Luke's gospel is that we, as His disciples, would "take care" to not be like those "kinds" of hearers who reject Him outright, or end-up falling away from Him later on. He would have us "take care" to hear His word and hold it fast no matter what may come. By cling to His word with great patience and endurance, we will eventually be fruitful --- which, after all, is what any good sower (or farmer) wants.
In this parable, Christ is that blessed Sower who loves us despite our many failings as His disciples. Christ daily and richly forgives our sins and will soon bring to completion that which he has begun within us.